1. Technical Field
The multiple embodiments disclosed herein relate to a method for controlling engine start in a vehicle.
2. Background Art
Hybrid electric vehicles (HEV's) utilize a combination of an internal combustion engine with an electric motor to provide the power needed to propel a vehicle. This arrangement provides improved fuel economy over a vehicle that has only an internal combustion engine. One method of improving the fuel economy in an HEV is to shutdown the engine during times that the engine operates inefficiently, and is not otherwise needed to propel the vehicle. In these situations, the electric motor is used to provide all of the power needed to propel the vehicle. When the driver power demand increases such that the electric motor can no longer provide enough power to meet the demand, or if the battery state of charge drops below a certain level, the engine must start quickly and smoothly in a manner that is nearly transparent to the driver.
Starting an engine in an HEV can occur when the vehicle is operating under any one of a number of different conditions. One such operating condition includes starting the engine in an HEV when it is moving under the power of the electric motor. Control of the engine start may be different for different sets of conditions under which the vehicle is operating.
Aging and other factors may cause the engine to fail to start on the first attempt. Among these factors are poor fuel quality, spark plug fouling, and reduced airflow through the intake system due to throttle sludging. By simply attempting a re-start of the engine under the same actuator command settings, these factors may not be overcome, resulting in multiple failed starts and the vehicle entering a non-functional state.
While the aforementioned description is focused on an HEV application, the authors recognize that the disclosed strategies can be applied to a conventional (non-HEV) engine start.